#? and !! in kotlin

1 messages · Page 1 of 1 (latest)

upper coral
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Can i know what are ? And !! In kotlin, idk if its only in kotlin or only spigotapi exclusive cuz i only use kotlin in spigot api, but they are related to something about the (Null) thing, and didn't find anything in google

tall salmonBOT
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<@&1008423204219531294> please have a look, thanks.

tall salmonBOT
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autumn echo
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google "kotlin null safety", they have a good official tutorial on it

upper coral
autumn echo
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essentially, !! the double-bang means
"if its null, throw" and makes a possibly nullable type into a non nullable

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Foo is non nullable
Foo? is nullable

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foo?.bar()
means "call bar() only if foo is not null"

upper coral
upper coral
autumn echo
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foo ?: bar
means "use foo, if its null, use bar instead", called the elvis operator

simple hedge
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Kotlin's docs are pretty good with this stuff, BTW

upper coral
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Like foo ?: bar.length and (foo) and (bar) are variables?

autumn echo
simple hedge
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references yes

autumn echo
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above example gets johns pet. but thats nullable, John might not have a pet

but then we do!! on it. so we require that pet exists (if it doesn't, it throws)

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so after doing that, pet is known to be non nullable

# 
val maybePet: Pet? =...
val definitelyPet: Pet = maybePet!!
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its all just shorthands for a bunch of null checks

upper coral
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Ok so "?" Is for declaring/assigning and "!!" For methods?

autumn echo
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Foo? is a nullable type

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foo?.bar()
calls methods only if its not null

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called safe-access

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foo ?: bar
is if-else

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the elvis operator

upper coral
autumn echo
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no

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!! throws an exception. it requires that its not null

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?. is "only do it if not null, otherwise don't do anything"

upper coral
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Yeah now i get it, i think

autumn echo
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the kotlin docs have great examples on this

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id suggest u read it first

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it answers all questions

upper coral
autumn echo
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if john has no pet, this code crashes when executed

simple hedge
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val foo:String?=null
val bar=foo!!.uppercase()

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run that 🙂

autumn echo
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with
pet?.bark()
it doesn't crash and simply doesn't bark

upper coral
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I think ill take your advice and read the docs

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Thanks for your help ❤️

autumn echo
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it also has the kotlin playground. so u can try it out and execute right there on the website

calm tangle
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Do you know java optionals?

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?: is like Optional#orElse

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?. Is like Optional#map or Optional#ifPresent depending on the usage

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And !! Is like Optional#orElseThrow

calm tangle
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Basically kotlin has Javas Optional API bundled into its syntax

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For compulsory null safety

upper coral
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found out the safe stuff in kotlin tho

upper coral
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also if somehere here knows spigotapi i would use some help

autumn echo
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we have a minecraft category when u ask a question here

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there are people who can help

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not too many, but some

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u just gotta ask a question and select minecraft 🙂

upper coral